Posted
by
timothyon Tuesday December 27, 2011 @11:50AM
from the seasonal-ferry-across-the-river-crab dept.

cswilly writes with the news that China's satellite navigation system, called Beidou, has been successfully activated. "With ten satellites now, 16 in 2012, and 35 in 2020, China is making damn sure they are independent of the U.S. military's lock on GPS. According to the article, 'Beidou, or 'Big Dipper,' would cover most parts of the Asia Pacific by next year and then the world by 2020.'" The BBC also has slightly more detailed coverage.

GPS can be spoofed now. It can't be long before wide spread spoofing and jamming takes place. Seems like they'll have to go back to navigating by landmarks. Perhaps they could use something like google earth that scans and recognizes the terrain where they are.

Not really a concern - the US can certainly shoot down all the satellites it wants to. Those in lower orbits like GPS and spy sats can be taken down by (relatively) cheap missiles launched from a jet at high altitude. They'd all be gone in the first few hours of a real war.

Not really a concern - the US can certainly shoot down all the satellites it wants to. Those in lower orbits like GPS and spy sats can be taken down by (relatively) cheap missiles launched from a jet at high altitude. They'd all be gone in the first few hours of a real war.

Our GPS Satellites are in Lower Earth Orbits. These BeiDou satellites are in Geosynchronous orbits, far outside of our missile range, and possibly for exactly this reason. Keep in mind that in that "real war" the process of destroying the few dozens of enemy satellites you want to destroy will produce enormous debris clouds through LEO, possibly destroying yet more satellites and causing yet more debris clouds. This sort of has a MAD effect, as such a shooting war could wipe out most of the planet's LEO rea

Shooting down GEO sats just takes a (much) more expensive rocket (though I suspect there's a MI(n)RV payload for just such a circumstance). I'd guess the plane-carried ABM lasers could fry a satellite in actual Star Wars style as well, if that program happened to be funded by whatever administration was in charge during the war - that's some really impressive technology.

They are very similar to the European Galileo satellites. They are similar to GPS, but use different frequencies than GPS.

Originally, China was involved with the development of the Galileo constellation. They backed out because they didn't feel like they had a big enough voice in its development.

The Chinese constellation, Compass, is intended to be as accurate as GPS. They will almost certainly have their constellation fully deployed long before Europe gets their act together and finishes the Galileo system

The Chinese Borg use lead-based nanoprobes and the eye lasers have a tendency to blow up.

Actually, the Chinese do have a lot of parallels with the Borg... steal technology rather than develop it themselves, a large supply of cheap labor, putting the collective ahead of the individual, funny colored skin...

From what I can tell from the Wikipedia article, Beidou is an active system where the "client" sends data to the satellites in orbit. It makes perfect sense for the Chinese though, because now they can track where their users are -- something not possible with the passive US system since the receivers only receive and can't transmit any data back. In short, Big Brother Beidou always knows where you are.

Seems like an active system has a huge disadvantage, though. You can DOS the satellites by pointing an antenna at each satellite and jamming their uplink frequencies, knocking out the whole system for everyone, everywhere. In the US system, you can only jam local terrestrial reception and anybody over the next hill won't be affected.

That was the "test" system. And their description is completely ass-backwards. I'm not sure how useful that would be for mobile units or wide spread use.

The terminal sends a signal to the satellites (say, 3 seconds latency due to distance). The satellites send the timestamps to a ground station (again, 3 seconds). They do some maths, then send the answers back to the satellites (again, 3 second), which send it back down to the terminals (finally, another 3 seconds). That is like 12 seconds, plus calculations, etc. Good luck using that info reasonably at 100+ KPH

That still leaves the issue of if terminals become popular, potentially MILLIONS of signals being broadcast skyward for the satellites to receive, sort, stamp and relay.

The Wikipedia article reads like an instruction manual on how NOT to do GPS. What am I missing?

The Beidou-1 satellites are Geo Stationary not LEO. That being said, according to Wikipedia [wikipedia.org] latency is about 1/4 of a second for each leg.

Still, the idea of transmitting potentially millions of signals blindly in the sky to a constellation of GEO satellites, and letting them do the work of sorting, stamping, and relaying seems a bit ass-backwards.Square Peg, meet Mssrs Round Hole and BFH.

Something I didn't realize until recently is that in the northern latitudes (Canada, northern US), GPS coverage has occasional small gaps in it. My John Deere dealer was saying that in some areas every few days about 6pm (happens to be that time in those areas) GPS coverage drops below 1 meter accuracy levels, and in those areas GPS guidance on farm machines becomes unusable for about an hour or so. As well sometimes a satellite goes offline for maintenance. As agriculture is becoming very reliant on GPS (hence John Deere lobbying in washington against LTE usage of adjacent frequencies), this is a problem. Because of this John Deere now uses GPS and GLONASS together to get better coverage. When Galileo provides coverage, it will use those signals too. The point is, more GPS systems simply improve reliability for everyone, if the Chinese allowed western use of their signals.

When we were traveling across the United States, there was about 45 minutes of our trip through Utah where we were not receiving GPS signals. I believe it happened in the early afternoon. Fortunately there were not turns involved during that portion of the trip.

Before GPS we used to use things called 'maps' and something given the fancy-pants name of 'dead reckoning' (figuring out where you are based on direction, average speed, and duration of travel). I am astonished that someone is complaining that they had a 45 minute window (75 km gap at 100 km/hour) where GPS was not available and were worried about getting lost.

Something I didn't realize until recently is that in the northern latitudes (Canada, northern US), GPS coverage has occasional small gaps in it.

It doesn't. The constellation's orbital pattern is uniform across the entire surface of the Earth.

My John Deere dealer was saying that in some areas every few days about 6pm (happens to be that time in those areas) GPS coverage drops below 1 meter accuracy levels, and in those areas GPS guidance on farm machines becomes unusable for about an hour or so.

Your John Deere dealer is a little shaky on how GPS operates. The birds are in 12 hour sidereal orbits, which means the pattern (as seen from an fixed location on Earth) repeats every 11 hours and 56 minutes.... Which means (if such an effect as he describes existed) it would steadily and regularly drift earlier through the day. Thus not only would the effect be seen 'about 6PM' every two weeks or so, but it would also be visible at varying times through the day for a week roughly every other week. (This also implies the gaps drift across the Earth's surface in a regular pattern, and would be visible in places other than the northern latitudes.) In addition, he may not realize that GPS accuracy *normally* varies somewhat over spans of a few hours as the geometry of the visible portion of the constellation varies. So what he's seeing is something else, amplified by observer bias.

As well sometimes a satellite goes offline for maintenance.

Yes, they do. But the system is designed and operated such that having a bird offline for maintenance degrades total system performance by only a very small amount.

As agriculture is becoming very reliant on GPS (hence John Deere lobbying in washington against LTE usage of adjacent frequencies), this is a problem.

The problem isn't the GPS system. The problem is John Deere is trying to use the system at an accuracy (100% availability at 1m) greater than the specified [civilian] performance levels (95% availability at 7m).

The problem isn't the GPS system. The problem is John Deere is trying to use the system at an accuracy (100% availability at 1m) greater than the specified [civilian] performance levels (95% availability at 7m).

While I can't speak as to the John Deere system in particular, most the Ag navigation systems are using WAAS on the low end and VRS RTK subscription systems on the high end.

Interesting. I wonder if talking to multiple systems, combined with an accuracy correction, can get the 100% 1 meter accuracy that ag desires. I guess the ag industry's needs is proof that GPS is somewhat inadequate, at least for their needs. Perhaps demand will drive a better overall positioning system.

The constellation's orbital pattern is uniform across the entire surface of the Earth.

Technically, yes, but this assumes you have good visibility of the sky. At high latitudes, especially when you're in cities/urban canyons (where you only have a narrow view of the sky & can't see the horizon), fewer satellites are visible (compared to closer to the equator)

Not "technically yes", but "actually yes". The high latitude effects only take hold North of 80 degrees, and the effect is not one of visibility bu

The good news is that it is rather easy these days to build equipment using multiple satellite positioning systems. The Apple 4S for example uses both GPS and Glonass, which is nice as Glonass apparently provides better coverage in western Europe. When Galileo goes live, we'll see circuitry for 3 systems. And at some point it'll be 4 when the Chinese one goes online.

Would be possible to get a more accurate position if a receiver combined the various GPS systems - as a kind of check/balance. For non-military use the GPS systems introduce inaccuracies. Is there an algorithm that would bring the resolution down from 10 meters to 1 meter or less?

No, GPS does not deliberately introduce inaccuracy - that was part of selective availability, which was turned off in 1998. What GPS does do is not make available to civilians the correction mechanism that enable military grade accuracy.The accuracy of civilian GPS units (within what's available from the system) is mostly dependent on factors outside of the government's control... The design of the antenna, how well it's matched to the re

AFAIK cm level accuracy requires differential GPS. Between 1 and 3 meters of the GPS error is due to atmospheric issues. By siting one receiver at a known point, and broadcasting the current 'location' your field instrument can correct it's idea of where you are.

In essence differential GPS is a local version of WAAS. The closer the receivers are, the better the accuracy.

Another trick is done by tracking the phase of the carriers. Requires much better electronics, and if you lose carrier sync you have to

Yes. This has been done for many years in survey equipment. a typical combination of Navstar (U.S. GPS)/GLONASS increases the number of satellites in view and therefore the accuracy. The biggest problem with combinging Navstar and GLONASS is that Navstar is CDMA (code division multiple access) while GLONASS is FDMA (frequency division multiple access). The former technique makes each satellite use a different "language" sort to say, while the later one uses different frequencies. The result is that a dual receiver needs two independent receivers, making them more expensive. New GLONASS satellites will start using CDMA signals in addition to the FDMA, so that legacy receivers work, and some time in the future new CDMA receivers can use both Navstar and GLONASS with a single type of tuner. Galileo was from the ground up designed to use CDMA and as a result, it is much easier to design a Navstar/Galileo dual receiver. As a matter of fact, many survey devices designed for Navstar can be upgraded via a firmware update to use Galileo as well. You can't upgrade to use GLONASS with a simple firmware update, you also need another tuner.Regarding accuracy, the thing is that you can't go much less than 5m by just adding more satellites. This is because this error is part of ionosphere delays, and more satellites can't correct this error. It is like trying to do a measurement by averaging 1000 readings, but all done with a bad ruler. At some point, you need to figure out how good your ruler is. And the problem is that this changes dynamically so standard Kalman filter techiques also stop being effective for better than 5m accuracy. There are two approaches for this: the first one is dual frequency, and this is in part how Galileo achieves better accuracy. The idea here is to exploit the dispersion property of the ionosphere. It works like this: different frequencies have different delays, so you send the same signal using different frequencies, measure the delay different, and solve for the ionosphere error. This is what survey-grade equipment do, but they do this by tracking the encrypted military P(Y) code, which is encrypted. The result is a dual frequency solution but full of hacks that make it unstable. This means, as soon as the signal is interrupted for a short time, you need to re-sync.The other approach for sub meter accuracy come from differential GPS. This technique uses to close receivers, one with a fixed known location. By measuring the error on the known location, you can apply corrections to the moving rover. But for this you need a link between the two (radio, UMTS, GSM, etc) or some post-processing. In addition, you need receivers capable of recording RAW data and then doing some complex math.The cream of the desert comes from using carrier-phase measurements. With this technique you can go up to cm accuracy. This requires tracking the actual carrier wave, and a very precise model of the earth or post-processing software. The accuracy comes at a price: very very unstable. You need clear blue sky and uninterrupted signals. Plus about 20 seconds to lock the signal, even after small interruptions.So to answer your question: more satellites guarantee better consistency and readings, particularly in cities and urban landscape. But you can't go below 5m unless you enter differential GPS or dual frequency measurements.

Carrier tracking does not require a very precise model of the earth. Real Time Kinnematic GPS has been done for well over a decade with rather sane processing requirements. It also isn't unstable. So long as the L1 and L2 signal of five satellites are tracked one can initialize on the fly, and you only need to track four continuously to maintain said initialization.

Like differential (a code-base correction) kinnematic requires a base receiver and a rover receiver. They can either be in real time c

GPS horizontal positioning does not require a very precise model of the earth.

GPS vertical positioning does not require a very precise model of the earth.

The gotcha there is that GPS works in ellipsoidal heights, NOT elevation. The ellipsoid is a simplified model of the earth. Elevation is height above mean sea level if the sea reached where you are. The elevation of any point measured by GPS is a combination of the ellipsoidal height and a gra

If the China system does not have the same DOP setup then it will be easy for hackers to use two receivers to read a location from both and create a correctional signal or negate the DOP that the Us military puts on the US GPS system. Giving the TERRORISTS ultra precise coordinates to invoke their TERROR

The U.S. has theirs, China just went online, the Russians also have their own and the EU is also planning one. While I can certainly see why each country (or interest) would like to have their own to prevent being locked out - c'mon. What a huge waste of money and resources that could surely be spent in better ways. Then again, militaries have never really been known for their altruistic interests.

Yes. The US GPS system has never been the only game in town. If they want to add their own, fine, go ahead. I'd love to have more navigational systems that are publicly avaliable so that receivers could be more reliable and acurate. The European system is not going to be fully functional for some time. The Russian Glonas system has global coverage but is not nearly as acurate as the US system in most cases, but they are upgrading it now. They only started coming out consumer-level with combined GP

The U.S. has theirs, China just went online, the Russians also have their own and the EU is also planning one. [...] What a huge waste of money and resources that could surely be spent in better ways.

Good point. Maybe the US, China, and the USSR could share a single collection of tanks and jet fighters as well. That would cut out a lot of redundancy, and also save fuel when a war started, since there would be no need to transport weaponry across the globe to fight -- it would all already be colocated together in the same hangar, so they could just start firing at each other right away.

I wouldn't trust those clods with printed maps (which are all censored to suit their tastes) so why on earth would I trust them to not only provide me with nav data, but to have the ability to track my receiver? Jeebus....

All this while the vast majority of their country lives in what most first world countries would consider abject poverty.

China has a huge amount of their own infrastructure, so this isn't really surprising. Unlike U.S., China likes to do everything themselves. This also means you're not dependent on other countries like the U.S. is. What you don't understand is that China thinks long term, and everything they've done will grant them the leading country status some day, probably even within 10-15 years, especially when considering how much U.S. and EU are struggling now after thinking only short term financial gains.

It is also part of China's culture. The Chinese tend to prefer isolationism and doing things themselves. Where in the short term (The next 20-50 years) does have advantages however in the long term if it ends up cutting themselves from the rest of the world may bring them back to their third world status again.The United States has some of this in our culture, however the US culture tends to have a Duality in its culture which is often confused with being a nation of Hippocrates. So while we will open

You are forgetting the main driver in China. It's not money but the big centralized party.
Let's look into the future to see if the rich people will succeed in taking over the power (like in the west) or it will be the government keeping the power over oligarchs (Russia).

That would be extremely uncharacteristic of China. We're talking about a civilization that built an 1100 mile long canal over a period of 1000 years or so. China has been doing long term planning, especially infrastructure planning, for an incredibly long time. That canal project started in the 5th century BC.
http://en.wikipedia.org/wiki/Grand_Canal_(China) [wikipedia.org]

Who does the US rely on for GPS? Only themselves of course, so this isn't exactly a good example.

Within 10-15 years, China will be deeply effected by their housing bubble as Japan was in the 90s. Unlike Japan, the primary thing maintaining social stability in China is continued economic growth. Without this, China will be facing very serious internal problems.

I recently read a Chinese article about how many celebrities in China have dual citizenship so that they can leave the country quickly. Many political

Just as important, 8 of the 9 members of the PolitBuro Standing Committee (the highest and most powerful decision-making body in China) are engineers by profession. The most popular profession in the US Congress is lawyer.

China has a huge amount of their own infrastructure, so this isn't really surprising. Unlike U.S., China likes to do everything themselves. This also means you're not dependent on other countries like the U.S. is. What you don't understand is that China thinks long term, and everything they've done will grant them the leading country status some day, probably even within 10-15 years, especially when considering how much U.S. and EU are struggling now after thinking only short term financial gains.

China may like to do everything themselves, they still are extremely dependent upon the West's desire for goods made in China. Will China's middle class grow to the point that China will no longer need USA or Europe to buy their stuff in 10-15 years? I doubt it.

Umm... you are aware of the differences between China and Japan, right?

Such as, say, a massive difference in population? A massive difference in natural resources? The fact that China is now locking up energy and mineral resources around the world which will deny their use to the USA in 50 years?

China and Japan are in no way comparable in this sense. You WILL be second fiddle to China. You can like this or not, but that's the simple reality. You almost are already. You will be passed within a few years, and continue your downward slide as the world aligns more and more to the number one world power of the future: China.

Not this shit again. It looks like the shills from China are getting to the point where they even infect Slashdot.

Want to know one thing China lacks? The ability to grow food for its people. As of now, they are an exporter. Give it 10 years, and that isn't going to be the case. If the US gives a middle finger to the world, the country can keep its population fed. May not have the variety, but people would survive. Other countries would have mass starvations if it wasn't for their imports.

We have heard the second fiddle to China thing before. We were going to forever be second fiddle to Japan. We were going to be swallowed up by Communist countries because the USSR had so much land, puppet governments, and did not hesitate to use brutal force when called on. We were going to be swallowed up by every nation in the world going under Sharia law.

Not to say China isn't doing their part. The one thing China is good at is sabotage. They are going ape-shit dumping solar panels for way below the cost of materials + labor in the US market in effort to kill that industry and take it over for themselves. Instead of innovation, this is how they go about doing things. Hopefully in the fall of next year, we get a Congress elected that actually abide their oath of office and actively stop this crap.

The US has its faults. In fact, sometimes you wonder what the country does right, but like a NoSQL database where you wonder where the hell the consistency comes from but keeps its integrity over a period of time, the US keeps going.

Ahhhh, I've heard this. You need to check with your minister of demographics.

How many people in China will be over 65 in the year 2025? How many people, as a percentage, will that be?

The great Chinese economic expansion will be quickly followed by the great Chinese population implosion due to not enough young Chinese. In fact, you'll be able to watch as Russia goes through this implosion right before China so you have a taste of what's to come.

Umm... you are aware of the differences between China and Japan, right?

Population really isnt the determining factor that people are making it out to be. Economic freedom is what its all about and countries with lots of it end up with similar purchasing powers and standards of living. E.U. with its $30K/person, South Korea and Israel with their $31K/person, Japan and Taiwan with their $34K/person, Canada with its $40K/person, U.S.A with its $48K/person.

China is at $8K/person and there is nothing that they can do about it without becoming just like the rest of us. Does it ma

Too bad the GDP per capita isn't a measure of "a better life".The percentage of obese people, social inequalities, illiteracy, life expectation and pollution should probably be taken into account, among others.http://en.wikipedia.org/wiki/Human_Development_Index [wikipedia.org]GDP and growths are pretty arbitrary "measurements" and aren't really linked to anything physical.

Well, sort of. The top GDP nation in that graph, at $58K, has the same HDI as some other nation with a GDP of under $20K! That is really striking. Above $30K, I see no overal trend of increased HDI at all.

With GapMinder you can set the scale for GDP/Capita axis to logarithmic, which is really what such a metric should be (economic growth is exponential.)

Instead of the regression curve that levels off, its a straight line from one corner to the opposite. This cannot be explained by any other means other than that GDP/Capita is really a very good proxy for HDI.

You also wont have the same argument about those two countries with a logarithmic GDP/Capita, but you might then notice that Equatorial Guinea is a

I'm old enough to have seen all the reports of Japan and Latin America rising to topple the United States as dominant power. I agree with you that China will likely fail (most of their books are cooked, the next generation is all but completely sterile due to God knows what pollution).

But that just leads to another question: WHEN will the United States implode? I can think of at least a dozen opportunities for it to simply fail and fail hard. Many other nations have failed due to less.

I'd say it's already started, but the decline is a slow process. Empires don't so much fall as decay. It took longer for the Roman Empire to completely fall than the United States has even existed. If you want to put a timeline on it, I'd say the decline started post-WW2. We had a good run shortly after as the sole manufacturing powerhouse of the world, but that wasn't going to last forever.

Bear in mind we are *still* one of the biggest centers of industry in the entire world though. We're just having

Post-WW2? China was a piddling country recovering from being ravaged by Japan and colonial powers. Total war had left Europe in pieces. And so forth. The U.S. and Russia were the big players as the U.S. was untouched by war on its lands and Russia had been (mostly) shielded by its Winter. The rest of the world has either recovered or has begun rising to the standards of everyone else, thus exaggerating the "fall" of the U.S.

USSR was so well shielded by its winter that it suffered more casualties than any other country, the greatest number of civilian casualties (far more than died in the Holocaust), and the total annihilation of several of its largest cities? It seems the only thing the US lost in comparable quantity was the ability to teach history...

Freedom. Individual Americans have the freedom to discuss and try things, even unpopular or politically- or economically-incorrect alternatives to the current paradigm. Flexibility. When that which is popular or politically ascendant or otherwise "approved" turns out to be wrong, the alternatives are eventually tried. Unfree societies stamp out "error" and inflexible ones don't accept change.

Freedom. Individual Americans have the freedom to discuss and try things, even unpopular or politically- or economically-incorrect alternatives to the current paradigm. Flexibility. When that which is popular or politically ascendant or otherwise "approved" turns out to be wrong, the alternatives are eventually tried. Unfree societies stamp out "error" and inflexible ones don't accept change.

Are you sure you want to make that statement? There are tons of things you cannot do in the U.S., restricted by either laws or socially. There are things that are completely frowned upon by U.S. but that are lawful, ok and even normal things elsewhere. Hell, U.S. even thinks there's something wrong with nudity while at the same time promotes violence. There are also countless amount of things that are restricted by laws, and discussing and promoting certain views are also limited. For example, U.S. tries ve

Equivocation fallacy. There is no way to compare the regime of censorship in China with that in the US. In the United States, things like nudity may be "taboo", but the fact is, unless you get into child pornography or threaten to kill the President, nobody from the government will give you any trouble whatsoever.

I could say any number of things in this very post that would get me arrested in China. Conversely, short of posting direct threats or incitements to violence, I can't think of anything I could

With the dollar dropping by half in value, they've lost 500 billion dollars in purchasing power.

They do this to keep products cheap enough to sell to the US so they population has work and won't get antsy. They build empty cities for similar reasons (well actually I can't comprehend exactly why they build empty cities and empty buildings- it seems goofy).

China being a huge country is not an asset, it's a liability.

They do have a good legal lock on assets- but many of those assets are only rare at the current prices. As soon as rare earth prices go up 50%, millions of tons of rare earth can come on line- including a huge mine in the US.

About the time they stop building empty cities, the demand for copper and other building materials is going to drop through the floor.

--

The US leadership class appears to have lost it and descended into greed.

--The true threat to the work is not china or the US but the corporations and the top 1%. And it's almost certainly two decades too late to do anything about it.

Satellites in geosynchronous orbit make poor spy satellites, for one they are stationary in relation to the ground so you have to look at an angle to see anything increasing the atmospheric distortion, they are also up much higher which also increases the distortion, and thirdly because they are stationary they are much easier targets for satellite weapons as height is their only protection. While permanently positioning a satellite over a test bed would seem like a great idea, either the test site is comp

First, the word you're looking for is geostationary. Not all geosynchronous orbits are geostationary.

Second GPS cannot be done with geostationary orbits. You have to have a minimum of three non-collinear points to triangulate a location on the surface of the Earth, and geostationary orbits are effectively collinear for all practical purposes. As such, geostationary orbits would only get you longitude (position along that orbital line), not latitude.

Okay where to start.1. Navigation satellites are not in geosynchronous orbit to start with so what does that have to do with anything?2. There are more than one type of "spy" satellite. Imaging is only type. Elint and Sigint satellites are often in geosynchronous orbit. They site over a country hovering up all the radio transmissions that it can including things like radar.

So would these make good spy satellites? That depends on what you mean by spying? For some missions they may have a use. Even a relativ